1. Field of the Invention
The invention relates to a method for positioning a mobile device, and more particularly to, a method for positioning a mobile device in a wireless wide area network (WWAN).
2. Description of Related Art
In recent years, many studies have discussed about positioning a mobile device under a wireless positioning system. Wireless positioning technology has included many methods, such as signal strength (SS), time of arrival (TOA), angle of arrival (AOA), time difference of arrival (TDOA), and so forth. The signal strength (SS) utilizes a conventional signal attenuation model to calculate distances. The time of arrival (TOA) positioning method measures a transmission time of a wireless signal between the mobile device and a base station. The angle of arrival (AOA) method utilizes a measurement of an antenna array obtaining angle of a serving base station (Serving BS). The time difference of arrival (TDOA) method measures a time difference between signal transmissions. The angle measurement at least requires two base stations and is not required to perform time synchronization. The time measurement at least requires three base stations, and even though is required to perform synchronization.
Wireless positioning technology has many applications including an emergency rescue and an intelligent transportation system. The emergency rescue requires accurately knowing a telephone number and a position of an assistance recipient; while, the intelligent transportation system is the transportation system of the next generation which combines traditional transportation system, electronic technology, control, computer, and management strategy. The intelligent transportation system utilizes the positioning technology to enhance efficiency and safety of the transportation system, reduce traffic congestion and improving charge reliably.
Non-line-of-sight (NLOS) is considered to be a most critical factor in influencing the wireless positioning technology. Since the signal transmission is to encounter with a reflection and a diffraction, the non-line-of-sight transmission may causes errors in the time measurement and the angle measurement. For example, a system of the time measurement may measure a transmission delay time, and a system of the angle measurement may measure a direction of a scattering point or a disruptor. There once was an experiment performed under an IS-95 CDMA system, the non-line-of-sight errors are able to reach as much as up to 589 meters. Therefore, many studies are dedicated to reduce an influence of the non-line-of-sight errors.